Control of backward-facing step flow using burst modulation with a DBD plasma actuator

Abstract

In this paper, an experimental study is performed for channel flow over a backward-facing step, with a dielectric barrier discharge (DBD) plasma actuator (PA) as a flow control device that introduces periodic disturbance to the system. The plasma actuator is installed on the corner edge of the step, and it is operated by burst modulated or continuous waveforms. The Reynolds number Re based on the mean velocity and the hydraulic diameter of the inlet channel ranges from 2.0 × 103 to 5.5 × 103. The static pressure distribution on the lower wall behind the step is measured, and the pressure improvement coefficient is evaluated. The flow field around the step is examined by flow visualization using a high-speed camera, and the velocity profiles are measured using a particle image velocimetry (PIV) system. As a result, the pressure improvement coefficient increases with the induced flow due to the PA. The effect becomes increasingly significant as the duty ratio increases; however, the pressure improvement coefficient obtained with burst modulation is smaller than that with continuous modulation. An exception to this observation is obtained with the burst frequency fb = 500 Hz, duty ratio D = 50%, and Re ≤ 3.5 × 103. A reattachment length reduction of approximately 70 % is achieved with fb = 100 Hz, D = 75%, and Re = 2.0 × 103, when compared with the non-control flow scenario. The reduction rate is larger than that of the continuous waveform, and a reduction in reattachment length due to counter-clockwise vortices is observed on the upper side of the channel.

Keywords

• backward-facing step flow
• plasma actuator
• burst modulation
• pressure distribution
• velocity profile